Let me answer this from the perspective of someone who lives in a small European country. I find myself constantly in the position that sellers are abroad. In my experience it does not necesseraly make a fundamental difference in what country the other side of the transaction resides; you need to apply the same level of care.
Would you send a 5,000 USD check to someone you don't know hoping to eventually receive the merchandise? I wouldn't, whether in the same country or not. BTW, PayPal acounts are open to non-US residents as well.
On the other hand, if the seller has enough positive feedback and the amount at stake is reasonable small, there shouldn't be much difference between a US only or an international transaction. FedEx, UPS and the postal system work the same way in the US or in European countries. It only gets more complex if you need to return the merchandise for some reason, because of all the red tape involved in avoiding double import taxes and value added taxes and what have you.
Also, you need to be aware that some products are not 100% identical in different countries (apart from the obvious difference in voltages and A/C plugs). Warranties are also not usually transferable between foreign countries and the US. It depends very much on the manufacturer or distributor whether a product that was not imported or sold through the official chain even gets serviced.
In the last four weeks a bought a cable from an Audiogon member for USD 350, paid through PayPal, and he shipped the cable through USPS. Painless transaction. I also bought cables from a manufacturer for a five digit amount. Wire transfer worked without any problems (it took one day). It took two days for FedEx to ship the goods from the US to Switzerland.
